Laves phase-strengthened austenitic steels

Iron-based austenitic steels strengthened with Laves-phase precipitates, and alloyed with aluminum for improved oxidation resistance are potential candidate materials for fossil fuel energy systems operating at temperatures ≥800°C. This project is examining the microstructure and deformation structure after creep testing of such two alloys developed by the Oak Ridge National Laboratory (ORNL), DAFA 26 and DAFA 29. The project includes determining the mechanism of NiAl co-precipitation with the Laves phase precipitates, and how these two kinds of precipitates together with L12-structure Ni3(Al,Ti) precipitates affect the mechanical behavior. The project will determine both the precipitation mechanisms and the interaction of gliding dislocations with these precipitates by performing annealing studies for a variety of times and temperatures, and both room-temperature tensile tests and elevated-temperature creep tests (performed at ORNL) on these materials followed by post-mortem transmission electron microscope (TEM) examination. The orientation relationships between the phases are being studied using electron diffraction in the TEM. The precipitation processes and the deformation mechanisms will be further elucidated by performing in situ annealing studies and in situ straining studies in the TEM, respectively, at a variety of temperatures. This research is funded by the Department of Energy, National Energy Technology Laboratory.